bug#40611: Fontification of source bufffer can make Occur very slow (Emacs 27.0.90 pretest)

[Konrad Podczeck]

Open a latex file for which "M-x occur Ret the Ret" gives about 3000 hits. If 
the source buffer is fontified, it takes about 2 seconds until the occur-buffer 
pops up, a time that is about 7 times longer than starting the Emacs app! On 
the other hand, without fontification of the source buffer, the occur buffer 
pops up almost immediately. Setting the user option "occur-mode-hook" to nil 
has no effect on this difference.

Konrad Podczeck